Fluid inclusion studies in apatite of the Sung Valley carbonatite complex, NE India: evidence of melt-fluid immiscibility

Abstract

The Sung Valley carbonatite complex of Cretaceous age has a core of serpentinized peridotite rimmed by pyroxenite. The complex is intruded by small- to medium-sized bodies of uncompahgrite, ijolite, syenite and carbonatite. Apatite grains in the apatite-magnetite sovite are characterized by three varieties of apparently syngenetic primary inclusions: the type S (solidified) inclusions contain highly birefringent and anisotropic solids along with some gas and liquid; the co-existing type F (fluid) inclusions are of two types - low to moderate salinity gas-liquid inclusions (gas=15 to 35% by volume) and high salinity gas-liquid inclusions with one or more daughter minerals (halite, sylvite, carbonates). The large variation in homogenization temperatures between type S and type F inclusions and the difference in their composition are interpreted to be the result of a liquid immiscibility between a volatile-rich carbonate melt and a saline aqueous fluid. -from Authors